This invention relates to the field of implantable medical devices and, more particularly, to detection of micro-dislodgment of a pacing lead electrode at a heart tissue/pacing lead electrode interface.
Implantable pulse generators (IPG) are currently being used for cardiac pacemakers, defibrillator, and cardioverter applications. Such devices typically employ one or more pacing leads that connect the IPG with endocardial, epicardium or intravascular tissue using one or more electrodes coupled to the pacing leads. A pacemaker, for example, employs an IPG for purposes of pacing a patient""s heart, and may perform critical functions without which the patient may die nearly immediately.
A problem common to such IPG devices concerns changes that may occur at the electrode/heart tissue interface which may adversely affect the transmission of electrical stimulating pulses needed to properly pace the heart. An unsatisfactory lead placement of the lead, for example, may negatively influence the ability of the lead to transmit energy between the IPG and heart tissue via the heart tissue/pacing lead electrode interface.
Several techniques have been developed to evaluate the heart tissue/pacing lead electrode interface. U.S. Pat. No. 5,003,975 to Hafelfinger et al. provides a good description of various prior art solutions, including those described in U.S. Pat. No. 4,140,131 to Dutcher et al.; U.S. Pat. No. 4,549,548 to Wittkampf et al.; and U.S. Pat. No. 4,606,349 to Livingston et al.; each of which is hereby incorporated by reference in its entirety. Prior art techniques involving sensing and using lead impedance for determining the adequacy of lead conductor connections to the heart may be found in U.S. Pat. No. 5,534,018 to Walhstrand et al; U.S. Pat. No. 5,201,865 to Kuehn; U.S. Pat. No. 5,201,808 to Steinhaus et al.; U.S. Pat. No. 5,156,149 to Hudrlik; U.S. Pat. No. 5,137,021 to Wayne et al.; U.S. Pat. No. 4,899,750 to Ekwall; U.S. Pat. No. 5,184,614 Collins; U.S. Pat. No. 5,350,410 to Kleks et al.; U.S. Pat. No. 5,431,692 to Hansen et al.; and U.S. Pat. No. 5,549,646 to Katz et al.; each of which is hereby incorporated by reference in its entirety.
Although some of the proposed techniques for evaluating the heart tissue/pacing lead electrode interface provide for the detection of gross problems, such prior art techniques are unable to detect subtle changes at the heart tissue/pacing lead electrode interface that may, over time, adversely affect the ability of the IPG to properly pace the heart.
Micro-dislodgment, for example, is generally understood as a failure mechanism which limits the ability of the pacing system to function properly in the patient. Micro-dislodgment may be viewed as a precursor to a serious or potentially catastrophic pacing failure condition. Micro-dislodgment is understood as an undesirable change occurring at the heart tissue/pacing lead electrode interface that adversely affects the ability of the IPG to cause depolarization via the heart tissue/pacing lead electrode interface. Micro-dislodgment is undetectable when visualized using available imaging technologies, such as a chest x-ray. It is important to appreciate that the ability to detect subtle undesirable changes at the heart tissue/pacing lead electrode interface (e.g., micro-dislodgment) well in advance of a significant or catastrophic failure condition provides a physician the opportunity to further test and evaluate a suspect lead placement and, if necessary, reposition, repair or replace a suspect lead prior to the occurrence of a potentially life threatening episode.
There exists a need for a method and apparatus for predicting and avoiding lead dislodgment. There exists a further need for such a method and apparatus that may be applied intraoperatively, at follow-up, or on an ambulatory basis.
The present invention is directed to an apparatus and method for detecting changes at a heart tissue/pacing lead electrode interface. In particular, the present invention is directed to an apparatus and method for detecting micro-dislodgment at a heart tissue/pacing lead electrode interface. The micro-dislodgment detection approach of the present invention may be employed to detect micro-dislodgment at a heart tissue/pacing lead electrode interface in any of the four heart chambers.
Detecting micro-dislodgment at a heart tissue/pacing lead electrode interface involves measuring a first pacing threshold parameter at a first time during a patient""s cardiac cycle and measuring a second pacing threshold parameter during a second time during the patient""s cardiac cycle. Measuring the first pacing threshold parameter involves measuring the first pacing threshold parameter after initiation of an atrial contraction but prior to any appreciable amount of ventricular contraction, such as after a delay of up to about 110 milliseconds (ms) subsequent to initiation of an atrial contraction. The second pacing threshold parameter is measured after initiation of an atrial contraction and after an appreciable amount of ventricular contraction, such as after a delay of about 100 ms to about 400 ms subsequent to initiation of an atrial contraction.
The first and second pacing threshold parameters are used to detect micro-dislodgment at the heart tissue/pacing lead electrode interface, such as by comparing a difference between the first and second pacing threshold parameters to a preestablished maximum allowable deviation value. A difference between the first and second pacing threshold parameters in excess of the preestablished maximum allowable deviation value indicates a problem at the lead electrode/heart tissue interface. In one embodiment, each of the first and second pacing threshold parameters is a pacing threshold voltage, and the preestablished maximum allowable deviation value is a voltage ranging from about 0.2 volts to about 2 volts or more.
Alternatively, detecting undesirable changes at a heart tissue/pacing lead electrode interface involves computing a ratio of the first pacing threshold parameter relative to the second pacing threshold parameter and comparing the computed ratio to a preestablished maximum allowable deviation value. A problem at the lead electrode/heart tissue interface is indicated by the computed ratio exceeding the preestablished maximum allowable deviation value. The preestablished maximum allowable deviation value is a percentage ranging from about 5% to about 100%.
The respective first and second measuring steps and the detecting step may be performed using an external programmer in cooperation with an implantable medical device or, alternatively, solely by the use of an implantable medical device comprising a pulse generator or with a pacing system analyzer or external pacemaker at time of implant. The respective first and second measuring steps and the detecting step may be performed during the implantation procedure of a pacing lead electrode at the heart tissue/pacing lead electrode interface. The respective first and second measuring steps and the detecting step may also be performed using an implantable medical device while the patient is ambulatory. Data indicative of micro-dislodgment may be stored in the implantable medical device and subsequently read out of memory at any time for evaluation by a physician.
An apparatus for detecting micro-dislodgment at a heart tissue/pacing lead electrode interface in accordance with an embodiment of the present invention includes an implantable medical device comprising a pulse generator and first and second pacing leads. In accordance with one embodiment of the present invention, a first electrode is coupled to the first pacing lead and is adapted for implantation in the right atrium of a patient""s heart. A second electrode is coupled to the second pacing lead and is adapted for implantation in the right ventricle of the heart. A microprocessor determines an occurrence of micro-dislodgment at the second electrode/right ventricle interface using a first pacing threshold parameter determined for the right ventricle prior to any appreciable contracting of the right ventricle and a second pacing threshold parameter determined for the right ventricle during appreciable contracting of the right ventricle.
The microprocessor may determine an occurrence of micro-dislodgment at the second electrode/right ventricle interface by comparing a difference between the first and second pacing threshold parameters to a preestablished maximum allowable deviation value in a manner previously described. Alternatively, the microprocessor may determine an occurrence of micro-dislodgment at the second electrode/right ventricle interface by computing a ratio of the first pacing threshold parameter relative to the second pacing threshold parameter and comparing the computed ratio to a preestablished maximum allowable deviation value in a manner previously described. It is understood that a similar micro-dislodgment detection apparatus and methodology may be implemented for left ventricular implants.
The microprocessor provided in the implantable medical device may further store data indicative of a detected occurrence of micro-dislodgment in a memory coupled thereto. The microprocessor coordinates transferring of the stored data from the memory to an external programmer. Alternatively, the microprocessor that coordinates the micro-dislodgment evaluation may be provided in an external programmer.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.